1. Field of the Invention
The present invention relates to a slip suppression control system for a vehicle which is configured to control a wheel driving power according to a wheel traction state on a road surface.
2. Description of the Related Art
Conventionally, there is proposed a traction controller configured to reduce an engine driving power to restore a drive wheel traction on a road surface (e.g., see Japanese Laid-Open Patent Application Publication No. Hei 7-103009). This controller uses traction control for retarding an ignition timing of the engine with respect to an optimal timing to reduce the driving power if an increase rate of an engine speed exceeds a predetermined start threshold, thus inhibiting a slip.
However, since it is determined whether or not the drive wheel is slipping on the road surface based on an increase rate of an engine speed, a wrong determination occurs, in which the drive wheel is slipping on the road surface if a detected value exceeds a threshold for some reason or other, despite the fact that the vehicle is actually driving stably. To avoid the wrong determination, the threshold may possibly be set larger. In that case, failure to detect a slip occurs, that is, it is determined that no slip occurs despite the fact that the drive wheel is slipping on the road surface. Thus, it is difficult to set the threshold to an optimal value. If the threshold is not a proper value, accuracy of determining a slip is reduced.